/*
Copyright 2021 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
Copyright 2021 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Go support for leveled logs, analogous to https://code.google.com/p/google-glog/
//
// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// File I/O for logs.

package klog

import (
	"errors"
	"fmt"
	"os"
	"os/user"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

// MaxSize is the maximum size of a log file in bytes.
var MaxSize uint64 = 1024 * 1024 * 1800

// logDirs lists the candidate directories for new log files.
var logDirs []string

func createLogDirs() {
	if logging.logDir != "" {
		logDirs = append(logDirs, logging.logDir)
	}
	logDirs = append(logDirs, os.TempDir())
}

var (
	pid      = os.Getpid()
	program  = filepath.Base(os.Args[0])
	host     = "unknownhost"
	userName = "unknownuser"
)

func init() {
	h, err := os.Hostname()
	if err == nil {
		host = shortHostname(h)
	}

	current, err := user.Current()
	if err == nil {
		userName = current.Username
	}

	// Sanitize userName since it may contain filepath separators on Windows.
	userName = strings.Replace(userName, `\`, "_", -1)
}

// shortHostname returns its argument, truncating at the first period.
// For instance, given "www.google.com" it returns "www".
func shortHostname(hostname string) string {
	if i := strings.Index(hostname, "."); i >= 0 {
		return hostname[:i]
	}
	return hostname
}

// logName returns a new log file name containing tag, with start time t, and
// the name for the symlink for tag.
func logName(tag string, t time.Time) (name, link string) {
	name = fmt.Sprintf("%s.%s.%s.log.%s.%04d%02d%02d-%02d%02d%02d.%d",
		program,
		host,
		userName,
		tag,
		t.Year(),
		t.Month(),
		t.Day(),
		t.Hour(),
		t.Minute(),
		t.Second(),
		pid)
	return name, program + "." + tag
}

var onceLogDirs sync.Once

// create creates a new log file and returns the file and its filename, which
// contains tag ("INFO", "FATAL", etc.) and t.  If the file is created
// successfully, create also attempts to update the symlink for that tag, ignoring
// errors.
// The startup argument indicates whether this is the initial startup of klog.
// If startup is true, existing files are opened for appending instead of truncated.
func create(tag string, t time.Time, startup bool) (f *os.File, filename string, err error) {
	if logging.logFile != "" {
		f, err := openOrCreate(logging.logFile, startup)
		if err == nil {
			return f, logging.logFile, nil
		}
		return nil, "", fmt.Errorf("log: unable to create log: %v", err)
	}
	onceLogDirs.Do(createLogDirs)
	if len(logDirs) == 0 {
		return nil, "", errors.New("log: no log dirs")
	}
	name, link := logName(tag, t)
	var lastErr error
	for _, dir := range logDirs {
		fname := filepath.Join(dir, name)
		f, err := openOrCreate(fname, startup)
		if err == nil {
			symlink := filepath.Join(dir, link)
			os.Remove(symlink)        // ignore err
			os.Symlink(name, symlink) // ignore err
			return f, fname, nil
		}
		lastErr = err
	}
	return nil, "", fmt.Errorf("log: cannot create log: %v", lastErr)
}

// The startup argument indicates whether this is the initial startup of klog.
// If startup is true, existing files are opened for appending instead of truncated.
func openOrCreate(name string, startup bool) (*os.File, error) {
	if startup {
		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
		return f, err
	}
	f, err := os.Create(name)
	return f, err
}
